In recent years, in order to comply with the requirements for high-speed large-capacity signal transmission, there have been developed signal transmission techniques using optical wiring in place of conventional electric wiring. As optical transmission lines, polymeric optical waveguides have been noticed from the standpoints of facilitated processing, low costs, high freedom of wiring and capability of high densification.
The polymeric optical waveguides are suitably in the form of a flexible optical waveguide having no hard substrate and, therefore, exhibiting a good flexibility in view of expected connection between wiring boards.
It has now been attempted to apply the flexible optical waveguides not only to the connection between wiring boards but also to various general equipments or parts such as hinged portions of foldable cellular phones and hinged portions for connecting a display and a body of note-type personal computers for which a flexible printed wiring board has been conventionally employed. For this reason, there is a demand for such flexible optical waveguides having excellent flexing property, heat resistance and transparency.
As the conventional flexible optical waveguides, there have been proposed, for example, polymeric optical waveguide films as described in Patent Document 1. The proposed polymeric optical waveguide films include a cladding layer and a core layer which are made of a deuterided or halogenated poly(meth)acrylate, and produced by a spin-coating method. As illustrated, waveguide losses of the polymeric optical waveguide films are 1.1 dB and 1.5 dB (per a wave guide length of 5 cm) as measured at a wavelength of 1.3 μm, and the waveguide loss in a non-bent state was the same as that in a bent state (refer to Examples 1 and 2 of the Patent Document 1). Although the Patent Document 1 describes merely the waveguide losses under non-bent and bent conditions as to a flexing property of the produced polymeric optical waveguide films, it fails to specify concrete measuring conditions such as a radius of curvature upon bending as well as results of repeated bending test. Therefore, the details of the conditions together with heat resistance and transparency of the obtained films are not apparent from the Patent Document 1.
As described above, there are conventionally unknown such flexible optical waveguides capable of satisfying excellent flexing property, heat resistance and transparency at the same time.
Patent Document 1: JP 3,249,340